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Before upgrading or migrating

When updating from one major Apache Tomcat version a newer one, please make
sure that the JVM that is installed on your system supports at least the
required Java version. While it is possible that older versions of Tomcat may
not be compatible with newer JVMs, all the currently supported Apache Tomcat
versions (7.0.x, 8.0.x, 8.5.x and 9.0.x) are known to run correctly on Java 8
JVMs.

When migrating from one major Tomcat version to another (e.g. from Tomcat 7
to Tomcat 8, or from Tomcat 8 to Tomcat 8.5),
you should not copy the configuration files from the old version
to the new version. The recommended approach is to start with the default
configuration of the new version of Apache Tomcat and to adjust it as necessary.

When migrating from one minor release to another minor release within the
same major release (e.g. from Tomcat 7.0.27 to Tomcat 7.0.28) you can retain the
configuration files, but you should check to see if any defaults have changed
and/or if any new elements have been added and adjust your configuration files
accordingly.

Migration Guides

For upgrading between 9.0.x versions, see the
upgrading section of the Tomcat
9.0.x Migration Guide.